This invention relates to clutch controls for motor vehicles and more particularly to clutch controls for motor vehicles which are equipped with manual shifting transmissions It is a characteristic of motor vehicles that engines develop low power and torque at slow rotational speeds. It is also well known that the sudden application of loads to engines results in uncomfortable vehicle accelerations, violent shocks and/or engine stalling.
For the above reasons, clutches are provided for changing transmission gear ratios, increasing engine speeds and gradually applying loads to engines during vehicle start-ups. The clutch controls are activated when the driver depresses the clutch pedal thereby causing the clutch bearing to be pushed or in certain applications to be pulled against the spinning clutch fingers and causing the clutch to de-couple the transmission from the engine. During these de-couplings, the driver is able to shift the transmission to different gear ratios.
Clutch operating controls consist of basically three types: (1) fully mechanical linkage consisting of cable or rods and an actuating fork that activates the clutch bearing, (2) a hybrid system that consists of an hydraulic master cylinder that is connected via a fluid line to a hydraulic slave cylinder mounted outside the clutch housing that activates a fork that moves the bearing against the spinning clutch fingers, and (3) a fully hydraulic system where the fork and the external slave cylinder from (2) above are replaced by a complex annular slave cylinder that has a hole in its center through which the transmission input shaft must pass which in response to driver's activation of the master cylinder concentrically pushes the clutch bearing into the spinning clutch fingers. This system is often designated as concentric slave cylinder system or CSC system. With the CSC system the thrust load applied to the clutch bearing is concentric to or coaxial with the centerline of the input shaft because the CSC completely surrounds the input shaft and quill.
One serious problem with the mechanical and hybrid systems is that the pivoting forks push the bearing against the spinning clutch fingers in an offset arcuate manner while swiveling on a pivot. This action results in harmful scraping motions between the bearing and fork and between the bearing and its support tube or quill. This inefficient type of motion results in noise, chatter, vibration, contamination, heat, need for greater clutching effort by the driver and eventually premature failure of the clutching system.
With the above disadvantages of the mechanical and hybrid systems (utilizing forks), it has been demonstrated and accepted by industry that an hydraulic system using a concentric slave cylinder, while usually more costly, is more efficient or desirable than systems using forks.
In my prior invention described in U.S. Pat. Nos. 4,601,374 and 4,620,625, a concentric (CSC) hydraulic actuator and release bearing is provided which is in co-axial relationship with the clutch. Although this invention eliminates the wear problem caused by offset loads of the fork and compensates for clutch wear, it nevertheless has several significant disadvantages which the present invention eliminates while preserving its advantages.
One disadvantage of my prior invention and other CSC units is that serviceability is difficult and expensive. The replacement or inspection of the CSC hydraulic actuator and release bearing requires disconnecting the drive shaft, removal of transmission, disassembly of the stationary bell housing from engine block and many associated lines and conduits and is therefore a major vehicle disassembly. This lengthy process is repeated in reverse order when maintenance or replacement is completed. This disadvantage prohibits preventative maintenance and increases a manufacturer's warranty costs as well as the costs of vehicle ownership.
Another disadvantage is that optimum designs of the CSC hydraulic actuator and bearing are often not possible because of the limited space inside of the bell housing.
Another disadvantage is that an annular actuating cylinder is required which is costly to manufacture and inspect and is therefore less reliable than conventional style cylinders.
Another disadvantage is that every CSC unit because of its having a large shaft hole in its center has two cylindrical surfaces that must be sealed against leakage of fluid out and must also be sealed to stop outside contamination from entering and damaging the two cylinders that form the annulus of the CSC unit. The sealing against fluid leakage is done by an annular piston seal. Thus, during actuation of the CSC annular piston, the movement of the annular piston seal on the two different and unequal sized sliding surfaces in each CSC unit tend to twist the seal and double the potential for wear, friction and leakage over conventional actuator seals that seal on only one sliding surface and that are therefore not subjected to uneven twisting loads.
The sealing of the CSC unit against road contaminants such as dust, dirt, water, salt, metal filings, etc. is also exceedingly difficult and inherently deficient. Unlike a conventional automotive actuator that uses a boot seal that hermetically seals the actuator against environmental contamination, the CSC unit, because of the large shaft hole in its center, can only be equipped with marginal labyrinth or wiper type seals making the CSC unit very vulnerable to failure from normal road contamination.
Another disadvantage is the design is not easily adaptable to the "pull type" type clutches which is becoming increasingly popular for high torque vehicles.
Another disadvantage is the high tooling costs of the annular hydraulic cylinder which is used in the hydraulic actuator.
With the foregoing in mind, it will be later appreciated that the present invention provides significant advantages and benefits heretofore unavailable.